1. Field of the Invention
The present invention relates to a mechanism and method for detecting the motion of a shaft. More specifically, the invention is a mechanism and method for detecting rotational and axial motion of a shaft, such as a shaft supporting a conditioner head.
2. Related Background Art
Chemical mechanical polishing (CMP) is conventional technology for flattening a surface of a semiconductor wafer such as a silicon wafer. To apply CMP to the surface of a semiconductor wafer, the semiconductor wafer is caused to slide against a polishing pad, while pressing the semiconductor wafer against a polishing surface of the polishing pad and providing a slurry containing a polishing agent and chemical reactant between the polishing pad and the semiconductor wafer.
In addition to the surface of the semiconductor wafer, the polishing surface of the polishing pad can also be flattened by repeated CMP processes. As a result, the surface roughness of the polishing pad decreases, which decreases in the efficiency of the CMP process. For this reason, many CMP devices have a pad conditioner for recovering the surface roughness of the polishing surface of the polishing pad. The pad conditioner restores the surface roughness of the polishing surface by bringing the polishing disk into contact with the polishing pad and rotating the polishing disk. The polishing disk is rotatably supported by a member called the “conditioner head,” and the conditioner head moves parallel to the polishing surface on the polishing pad by an arm attached to a CMP device.
Japanese Patent Application Publication No. H9-174420 describes a CMP device that has the pad conditioner mentioned above.